Thermocouples (TCs) are junctions of dissimilar metals conventionally in wire form. A DC voltage is generated at the junction which is a function of the temperature difference between the hot junction and the cold reference. This type of TC is relatively slow in response due to the mass of the wire junction and is not readily adapted to measuring surface temperatures, especially at temperatures above available glue attachment of thin wires to a surface.
Thin film thermocouples overcome the above-described speed and surface attachment disadvantages and have been described in the literature. One can deposit by evaporation or sputtering the metal alloys used in conventional wire TCs. See: Lepicovsky, J.; Bruckner, R. J.; and Smith, F. A. "Application of Thin Film Thermocouples to Localized Heat Transfer Measurements, AIAA paper 95-2834 (NASA TM-10745), 1995.
U.S. Pat. No. 4,969,956, "Transparent Thin Film Thermocouple", Kreider et al. Discloses a thin film thermocouple (TFTC) utilizing a junction of sputtered Indium tin oxide (ITO) and indium oxide (In.sub.2 O.sub.3) which claims an additional benefit of transparency. U.S. Pat. No. 5,356,485, Kreider, "Intermetallic Thermocouples" teaches the vapor deposition of intermetallic TCs. U.S. Pat. No. 5,708,233, Ochi et al., "Thermoelectric Semiconductor Material" teaches theoretical bases for selecting semiconductor materials for thermoelectric applications.
U.S. Pat. No. 5,616,266, entitled "Resistance Heating Element with Large Area, Thin Film and Method," issued Apr. 1, 1997 and co-pending patent application, Ser. No. 08/874,524, entitled "Method and Apparatus for Edge Heating of Thin Film Heating Element," filed Jun. 13, 1997, both assigned to assignee of the present patent application, disclose thin film resistance heating elements for use in a variety of oven and space heater applications. The thermocouple of the present invention may be used with the thin film heaters disclosed in these applications.